1. Technical Field
This disclosure generally relates to automatic data collection, in particular to readers and engines to optically read machine-readable symbols, for instance, linear or one-dimensional barcode symbols or two-dimensional area or matrix or stacked code symbols.
2. Description of the Related Art
Various types of readers are employed for reading machine-readable symbols, for instance, linear or one-dimensional barcode symbols or two-dimensional area or matrix or stacked code symbols. Some readers are fixed, for example, those found at grocery stores, supermarkets or other retail establishments, typically at the end of a conveyor belt. Some are portable, for example, handheld readers, typically found in warehouses and office environments. The handheld readers have housings, often with a rectangular shape or shaped as a pistol. The reader may be integrated into a terminal or other device, for instance, with various user input and/or output structures. User input structures may take the form of keypads, keyboards, buttons, user selectable icons, joysticks, thumb sticks, and/or microphones. User output devices may take the form of display screens (e.g., liquid crystal, organic liquid crystal), light emitting diodes, and/or speakers. Readers also typically include one or more communications systems to provide communications with external devices or systems. The communications systems may take the form of one or more radios and associated antennas. For instance, a reader may include a short range wireless radio, for example, one compliant with either BLUETOOTH or WIFI standards and protocols. Additionally or alternatively, the reader may have a longer range wireless radio, for instance, a radio that is compliant with a cellular communications system or network standard and/or protocol. The reader may additionally include one or more wired communications ports, for instance, a Universal Serial Bus® (USB) port, an Ethernet® port, a Firewire® port, and/or Thunderbolt® port.
Automatic data collection devices such as machine-readable symbol readers typically take one of two types, flood illumination systems or scanning spot based systems. Flood illumination systems either provide flood illumination of a target or rely on ambient lighting and capture an image (one- or two-dimensional) of the target. In contrast, scanning based systems sequentially scan a spot or point of light across a target, and produce a scan profile indicative of a magnitude of light returned from the target. The size of the spot is typically small, in order to provide sufficient resolution to read the machine-readable symbol, which is typically made up of patterns of two colors (e.g., black, white) although multi-color machine-readable symbols have been employed.
The machine-readable symbol reader may include one or more illumination or light sources to generate the flood illumination or the scanning spot. For example, the machine-readable symbol reader may include one or more light emitting diodes (i.e., LEDs) or one or more lasers (e.g., laser diodes). Laser light is collimated and coherent, advantageously keeping spot size relatively small over relatively long distances (e.g., 1-3 meters). Machine-readable symbol readers typically include one or more optical components, for example, lenses, mirrors, reflectors, prisms, dichroic mirrors. Scanning spot machine-readable symbol readers typically include one or more moving optical components to scan the light spot or beam in a defined pattern (e.g., raster scan pattern, Lissajous scan pattern). For instance, a scanning spot machine-readable symbol reader may include a rotating polygonal mirror or reflector, or a pivoting mirror or reflector. Pivoting mirrors or reflectors may pivot about one axis or two axes (e.g., perpendicular or orthogonal axes) to produce a desired scan pattern.
The machine-readable symbol reader may include one or more detectors which are responsive to light returned to the machine-readable symbol reader from the target. Detectors may, for example, include photodiodes, photosensors, CMOS optical sensors, or one- or two-dimensional arrays of charged coupled devices (CCDs), Vidicons, etc.
Often one or more of the illumination or light sources, moving optical components, if any, detectors and other optics (e.g., lenses, mirrors, reflectors, prisms, dichroic mirrors) are packaged in a unit commonly referred to as a scan engine. In use the scan engine may, for example, mount to a printed circuit board, for instance, a decode board which carries circuitry that decodes a scan pattern produced by the detectors. While denominated as a scan engine, such are not limited to scanning spot type machine-readable symbol readers, and the term scan engine as used herein and in the claims is not intended to be limited to scanning spot type machine-readable symbol readers.
Light leaving the reader is typically not visible as it passes through the environment (e.g., air), and may or may not be visible when striking the target. Consequently, some machine-readable symbol readers include an aiming beam mechanism, which projects an aiming beam which forms a visible pattern on the target. Such may facilitate aiming or orienting the machine-readable symbol reader with respect to the target or a position on the target. The aiming beam mechanism typically includes dedicated illumination or light sources, which is, or are, separate and distinct from the illumination or light sources that produce the scanning spot or beam. For example, the aiming beam may employ a different color light than the scanning spot or beam.
Often, the aiming beam mechanism is packaged as part of the scan engine. The size of the scan engine disadvantageously limits on how small the machine-reader imager may be made. An alternative approach that allows smaller scan engines, and hence smaller machine-readable symbol readers, is desirable.